Polythiophene thin films were deposited successfully on glass substrate by chemical bath deposition method using FeCl3 as an oxidant and chloroform as solvent. The effect of oxidant concentration on the properties of polythiophene thin films was studied. The surface morphology was influenced by oxidant concentration and deposition time. The oxidation concentration also strongly affects the optical properties of the polythiophene thin films. The transmittance decreases while the absorption, band gap and refractive index increases due to increase in oxidant concentration. (C) 2011 Elsevier B.V. All rights reserved.